Many oilseed grain products such as corn, sunflowers, and soybeans, and other types of vegetable products such as cocoa (referred to hereafter generally as products), have a substantial vegetable oil component. Often, this oil is extracted at some point while processing the raw products. The oil itself is often a valuable commercial material used in foods, plastics, etc. The solids remaining after extracting the oil are also valuable and can be used for both human and animal foods, as well as for other purposes. The process to be described was developed to form a part of a process for extracting cocoa oil from raw cocoa, but may be used in other vegetable oil extraction processes as well.
Early steps in the processing grind or otherwise change the form of the raw product to flakes, powder, or other types of particulate material. This particulate material is still permeated with most of the original natural oil. The oil is then extracted from this particulate material.
A number of different processes for removing or extracting the oil from this particulate material have been developed. The type of oil removal process of interest here is termed solvent extraction. After the raw product has been converted to particles, the particles are immersed in a hydrocarbon liquid solvent such as hexane, heptane, isohexane, butane, or any similar petroleum-based solvent that dissolves the oil.
Upon immersing the particles, the solvent forms a liquid solution with the oil in the particles. The oil-solvent solution is then removed from the particles in some manner, by for example, pressing or even simple gravity draining. In gravity draining, a screen supports the particulate material and allows the oil-solvent solution to drain through the screen to a catch basin. The solvent and oil are then separated with a conventional process. Usually, the solvent recovered during this separation step can be used again in the extraction process.
When extracting oil from certain kinds of products, such as flaked or ground cocoa, one process uses butane in a pressurized chamber to dissolve the oil. When pressurized at room temperature to perhaps 3.5 bars (50 psi.), butane is a liquid. At one atmosphere and room temperature, butane is a gas, well known as the fuel for backyard grills around the country. It is convenient for this process that the solvent (butane, e.g.) be a liquid at moderate pressure and room temperature, and a gas at room pressure, but the process can be used, less conveniently, with solvents other than butane that liquefy at different pressures or temperatures. Whatever solvent one chooses should not liquefy at a pressure or temperature that may change the properties of the product particles in an undesirable way. The solvent will be usually referred to hereafter as butane, but the processes should be understood to operate with a number of solvents that dissolve the product oil and have a liquid-gas phase change compatible with room temperature and pressure.
The pressurized butane solvent liquid forms a solution with the oil in the product, which can be drained from the flaked or ground product. Several stages of pressurized solvent extraction may be used to remove nearly all of the oil from the product particles. Depressurizing the butane-oil solution obtained in each stage boils off the butane which can then be reclaimed. The remaining oil can be used as a food constituent or for other purposes.
After the oil-solvent solution has been drained from the cocoa particles in the last stage, there is usually a significant amount of solvent still permeating the cocoa particles, perhaps 30% by weight, and a trace amount of oil. Where the particulate material will be used as human food or animal feed, it is important for a number of reasons to remove nearly all of the solvent from the particulate material.
First, the solvent may be toxic, so removing the solvent from the particulate material prevents harm to whomever or whatever might consume the end product of the process. Secondly, whether the solvent is toxic or not, it may be an air pollutant so it""s important to prevent as much of the solvent as possible from reaching the atmosphere. Third, the solvent is valuable. Extracting it from the particulate material allows its reuse in the oil extraction process.
U.S. Pat. No. 5,630,911 (Kratochwill) discloses apparatus and process for removing a substantial amount of the remaining solvent following gravity draining or other type of oil-solvent removal. The Kratochwill apparatus uses, within an enclosed vessel or volume, a number of inclined conveyors that carry the particulate material over heating plates. The particulate material permeated by the solvent still present is heated to vaporize the solvent. This solvent vapor can then be removed from the enclosed space. Some oil remains in the particulate material, but it forms a small percentage of the total mass. Kratochwill is incorporated by reference into this application.
One feature of the Kratochwill apparatus is that the process occurs at a temperature high enough to reduce the protein dispersability index (PDI) of particulate material having high protein content. A high PDI is preferred for some processed oilseed materials; for these materials, lower process temperature is an advantage.
A system for removing from a particle stream, a liquid such as a solvent that permeating the particle stream has at least two stages. The system includes a first vaporizing stage having a chamber where the pressure is maintained lower than the pressure of the entering particle mass. As the particles enter the chamber of the vaporizing stage, the lower pressure causes much of the liquid to vaporize. A pump removes the vapor, thereby maintaining the lower pressure in the vaporizing stage chamber.
A first stripping stage receives the particles from the first stage at a first particle inlet port and discharges the particles at a first particle outlet port. A first stripping gas inlet near the first particle outlet port injects an inert stripping gas into the particles. The inert gas mixes with remaining elements of the liquid and any entrained gas formed by the liquid, and the mixture is discharged at a gas outlet near the first particle outlet port.
A second stripping stage may also be present to receive the particle mass from the first stripping stage. The second stripping stage may have a construction different from the first stripping stage. In one embodiment, at least one of the stripping stages, preferably the second, transports the particle mass through gravitational force.
In one embodiment, the second stripping stage comprises a fluid removal chamber having a cylinder to be mounted in an approximately upright position. The cylinder has an enclosed passage from an upper opening to a lower opening. The cylinder has adjacent to the lower opening, a gas inlet into which an inert gas such as nitrogen can be introduced. We use the term xe2x80x9ccylinderxe2x80x9d here to mean any sort of hollow chamber having a cross section approximately constant along its axis. The cross section is often circular, but can also be square or other convenient shape. We intend the term xe2x80x9ccylinderxe2x80x9d to include chambers whose cross section varies somewhat along the axis, say where the chamber cross section tapers to become smaller toward the lower opening.
A particle outlet port forms a part of the lower opening of the cylinder. The particle outlet port regulates flow of particles from the cylinder at a predetermined flow rate. A source of pressurized inert gas is to be connected to provide pressurized gas to the gas inlet.